Abstracts

Rationale: Patients with childhood absence epilepsy (CAE) experience brief seizures characterized by 3-4 Hz spike and wave discharges on electroencephalogram (EEG). CAE represents approximately one sixth of all diagnosed childhood epilepsies, and causes impaired attention and social dysfunction in school-age children. There is increasing evidence demonstrating that behavioral impairments may persist in-between seizures, even when well controlled with medication. Our group previously examined such interictal deficits during behavioral testing using EEG-fMRI. Here we investigate relationships between variably impaired ictal attention and: (1) task difficulty; (2) seizure duration; (3) timing of task to seizure onset and end; and (4) interictal attention deficits. Methods: We tested attentional vigilance in patients (6-18 years old) with a diagnosis of CAE. Each subject underwent either a Repetitive Tapping Task (RTT) in which a button was pressed in response to letters presented on a screen once per second, or a more difficult Continuous Performance Task (CPT) in which a button was pressed when the target letter (X) appeared in a series of non-target letters, again displayed once per second. Both tasks were administered with simultaneous EEG-fMRI data collection (not discussed here). Ictal task performance was characterized by omission rate, commission rate, reaction time, d-prime, and beta, and related to interictal performance, seizure frequency, and seizure duration. Results: Out of a total of 90 children, 34 had absence seizures during behavioral testing (328 seizures during RTT and 323 during CPT). The mean seizure duration was 5.09±0.17 s (mean±SD). The mean ictal omission rate was 70% for CPT and 53% for RTT. For both RTT and CPT, ictal performance was weakly correlated with seizure duration; however, clear outliers exist in both tasks where longer seizures have spared performance and shorter seizures have very impaired performance. A weak positive correlation was also observed between ictal and interictal omission rates in both tasks. For RTT tasks, performance was relatively spared on average in the initial ~1s of seizures. For both CPT and RTT, performance deficits tended to recover towards the end of the seizure (last 1-2s). Conclusions: It is becoming increasingly clear that CAE patients sustain residual behavioral deficits in-between seizures, even when well controlled. CAE patients make a greater number of errors on sustained attention testing in the interictal period when compared to controls. Our data suggest that task difficulty and task timing have important effects on attention performance during absence seizures. Seizure duration is less consistently related to severity of deficits. Ictal attention impairment may be related to interictal deficits, suggesting chronic dysfunction in attention networks. This investigation will help us understand the neural mechanisms of attention deficits observed in CAE patients. In addition, further studies will examine the correlation between these behavioral patterns and EEG-fMRI data in the ictal and interictal periods.